Re: [RFC PATCH v3 00/10] Add support for shared PTEs across processes

[Jann Horn <jannh@google.com>]

On Wed, Oct 16, 2024 at 2:59 AM Anthony Yznaga
<anthony.yznaga@oracle.com> wrote:
> On 10/14/24 1:07 PM, Jann Horn wrote:
> > Second, there is a newer mode for IOMMUv2 stuff (using the
> > mmu_notifier_ops::invalidate_range callback), where the idea is that
> > you have secondary MMUs that share the normal page tables, and so you
> > basically send them invalidations at the same time you invalidate the
> > primary MMU for the process. I think that's the right fit for this
> > usecase; however, last I looked, this code was extremely broken (see
> > https://lore.kernel.org/lkml/CAG48ez2NQKVbv=yG_fq_jtZjf8Q=+Wy54FxcFrK_OujFg5BwSQ@mail.gmail.com/
> > for context). Unless that's changed in the meantime, I think someone
> > would have to fix that code before it can be relied on for new
> > usecases.
>
> Thank you for this background! Looks like there have since been some
> changes to the mmu notifiers, and the invalidate_range callback became
> arch_invalidate_secondary_tlbs. I'm currently looking into using it to
> flush all TLBs.

Ah, nice, that looks much better now. With the caveat that, from what
I can tell, the notifiers only work on x86/arm64/powerpc - I guess
maybe that infrastructure should be gated on a HAVE_... arch config
flag...